when you are looking for fans, on the label it will tell you how much air it will push/pull. You will need to figure out how much room you have and then get the fan(s) that will be able to exchange/remove that amount of air in an hour. Then once you have that figured out, you will want to place a couple of standing floor fans in your grow room to circulate that air before being removed. If your using 2 1000w HPS lights, im guessing that you have a fairly large grow area. You can get a rat cage fan (those fans that are in a circle and you can attach to the wall, get them at home depot, lowes, etc). Go to walmart and pick up a temp/humid battery thermometer and run your lights for 24 hours and look at what you have.
Hope that helps